(1) Field of the Invention
This invention relates, in general, to the use of hazardous waste material as an energy source in a cement kiln and, more particularly, to a method for utilizing solid hazardous waste material which permits the direct introduction of the solid hazardous waste material into the flame of the burning primary fuel in the kiln.
(2) Description of the Related Art
Numerous industries are faced with the challenge of how to properly dispose of waste materials, liquids or solids, that have been classified as "hazardous" because of its flammable or toxic nature. Environmental regulations prohibit the disposal of many hazardous waste materials in landfills. One alternative for the disposal of landfill-prohibited hazardous waste materials involves its incineration in specially equipped incinerators. Although effective, the use of specialized incinerators is costly and such incinerators are of limited availability.
As an alternative to the use of costly specialized incinerators, cement kilns have been designated by regulatory agencies as being suitable for the disposal of certain hazardous wastes. The high operating temperatures, long residence times, and the ability to provide favorable conditions for the chemical combination of inorganic residues of the waste materials into the active components of portland cement, make cement kilns ideal for the disposal of hazardous wastes. Furthermore, the burning of hazardous wastes in a cement kiln is beneficial to the kiln operator in that the hazardous waste material provides a rather inexpensive source of energy for maintaining the high temperature in the kiln which can significantly reduce the operating costs of the kiln.
Cement kiln operators have readily integrated the use of liquid hazardous waste materials into existing kiln operations. The liquid hazardous wastes are introduced into the burning zone of the kiln and are disposed of by incineration while serving as a source of energy for the kiln. Various attempts have also been made to utilize solid hazardous waste materials as a supplemental energy source in a kiln operation by introducing such materials into the burning zone of the kiln. Of course, it is important that the solid hazardous waste being utilized in such a manner also be incinerated in the burning zone according to environmental standards and regulations and not interfere with or adversely effect the formation of the cement clinker.
Some kiln operators have attempted to directly combine solid hazardous waste material with the supply of powdered coal that is used as the primary fuel source in the kiln. This method is not preferred because the solid hazardous waste material can cause the powdered coal to agglomerate into chunks which reduces its efficiency as a fuel source and because this method contaminates the entire coal supply. Furthermore, the introduction of solid hazardous wastes into the flame of the kiln burner in this manner can result in the creation of an undesirable flame length in the kiln which is detrimental to the production of quality cement clinker.
Others have introduced solid hazardous waste material as it is received from the producer directly into the flame of the kiln. In addition to potentially creating an undesirable flame length in the kiln, solid hazardous waste material as received from the producer often includes particles that do not instantaneously ignite when introduced into the burner flame because of the size of the particles. This is disadvantageous in that some of the solid waste material can come in contact with the cement raw materials before the waste materials are fully incinerated which can cause undesirable reducing conditions in the forming clinker. Still others have introduced a blended slurry of solid and liquid hazardous waste directly into the burning zone of the kiln, but also do not reduce the particle size of the solid hazardous waste materials prior to its introduction into the kiln resulting in similar undesirable effects.
Another method utilizing solid hazardous waste materials in cement kilns involves the containerization of the waste material in a sealed drum and subsequent introduction of the entire container into the interior of the kiln. Examples of such methods are disclosed in U.S. Pat. No. 4,850,290 (Benoit et al.) and U.S. Pat. No. 5,086,716 (Lafser). Such methods are costly in that they require the containerization of the solid hazardous waste in suitable containers and modification of the kiln to accommodate the introduction of the containers.
A need exists, therefore, for a method capable of conveniently and efficiently utilizing landfill-prohibited, solid hazardous wastes as an energy source in the operation of cement kilns that avoids the foregoing problems.